I've been presenting sessions on clustering Exchange Server at various Microsoft and third-party events for many years. After each presentation, at least one person has asked how Microsoft clusters Exchange, and how we maintain our 99.99% uptime. So, here's how we run Exchange 2003 at Microsoft:
Our internal IT department, Microsoft IT (MSIT) achieves high availability for its mission-critical e-mail infrastructure by utilizing systems and processes that are specifically designed for high availability, including:
For MSIT, the right combination of the above components helps to minimize planned downtime for maintenance or service pack installations. Unplanned downtime, whether caused by a server or other hardware failure, has also been reduced.
At Microsoft, the processes and technoligies that go into achieving 99.99% uptime can be broken down into three categories: Configuration (and Practices), Architecture, and Operations.
Of course, 99.99% uptime would not be achievable without continous learning, as well as adhering to and evolving of best practices. Maintaining high availability is an active, ongoing endeavor requiring continuous response and adaptation to new situations and technologies. All system measurements are regularly reviewed by management, and action must be taken to keep actual performance within the tolerances set.
If you're interested in designing or deploying your own highly available Exchange 2003-based messaging infrastructure, check out the Exchange Server 2003 High Availability Guide.